1. Technical Field
The present disclosure relates to a virtual base station apparatus and a communication method for performing millimeter-wave band communication using beamforming.
2. Description of the Related Art
In recent years, to ensure a bandwidth of 1 GHz or higher to meet rapidly increasing traffic demands, studies have been made on the employment of small base station apparatuses that perform communication by using millimeter wave bands. For example, a communication system (also sometimes referred to as a heterogeneous network) is conceived in which a plurality of small base station apparatuses are located within a communication area of a base station apparatus that performs communication by using microwave bands.
Such small base station apparatuses use millimeter wave bands. Communication using the millimeter wave bands causes propagation loss greater than that using the microwave bands, and it is difficult to extend the arrival range of radio waves.
One of the methods for reducing propagation loss, increasing the communication speed, increasing the cell area, and so on is directional control (beamforming) for a base station apparatus and a terminal (also sometimes referred to as a “terminal apparatus” or “station (STA)”) by using a plurality of antenna elements (antenna array). In transmission using directional control, a transmitting apparatus (base station apparatus or terminal) directs radio waves toward a communication partner, thereby allowing the radio waves to reach farther than in non-directional transmission. Thus, the cell area that is covered can be extended. In addition, since communication using directional control improves the signal to interference-plus-noise power ratio (SINR), the application of a modulation scheme and coding rate with high frequency use efficiency results in high transmission speed communication (see, for example, Institute of Electrical and Electronics Engineers (IEEE) 802.11ad-2012 Standard for Information Technology—Telecommunications and Information Exchange between Systems—Local and Metropolitan Area Networks—Specific Requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 3: Enhancements for Very High Throughput in the 60 GHz Band).
Directional control requires a base station apparatus to perform beamforming training for directivity matching for each terminal to be connected. In the beamforming training, the base station apparatus needs to have directivity (scan) over a wider angle to increase the cell area that is covered, and the time required for the beamforming training becomes overhead, resulting in a reduction in frequency use efficiency.